The present invention relates to a copier, laser printer, facsimile apparatus or similar image forming apparatus and, more particularly, to a developer aging method for a developing device included in such an image forming apparatus.
It is a common practice with an image forming apparatus to age a developer at the time of installation of the apparatus at the user's station or at the time of periodic maintenance of the apparatus. Aging is effected via the agitation of a developer initially introduced into the apparatus or the replenishment or consumption of toner. Aging provides the developer with a desired developing characteristic and thereby insures high image quality.
A two-ingredient type developer applicable to an image forming apparatus consists of toner and carrier. Generally, the amount of charge deposited on this type of developer varies, depending on the environment at the time of preparation, the duration of an unused state, and so forth. Specifically, even when an image is output under the same conditions as at the time of the initial introduction of the developer, image density changes with a change in the kind of the developer and a change in the environment of use. As a result, image density is apt to be excessively low, or in the worst case a locally omitted image or similar defective image and carrier deposition occur.
To solve the above problem, a developing device may be continuously driven for a preselected period of time in order to agitate the developer introduced therein. Alternatively, a paper may actually be conveyed through the apparatus in the same manner as during usual image formation. However, the conventional agitation scheme simply agitates the developer and cannot perform accurate adjustment implementing a desired developing characteristic. Toner replenishment to occur after this kind of aging is apt to cause the toner to fly about and even bring about defective images, image density variation, and other troubles. These troubles are particularly serious when the charging characteristic of the toner existing in the initial developer and that of fresh toner to be replenished are different from each other. The scheme actually conveying a paper, as stated above, wastes papers. Moreover, because this kind of scheme relies on usual toner replenishment control, a system of the type detecting the amount of toner deposited on a photoconductive element with, e.g., an optical sensor for the replenishment of toner will replenish toner continuously as long as the developing ability of the developer is low. This prevents the charge of the toner from being sufficiently increased and causes the toner to fly about and contaminate the background of the photoconductive element. In addition, if the developing ability of the initial developer is high, a great amount of toner is deposited on the photoconductive element and causes the aging to complete without any fresh toner replenished due to the inherent control. As a result, when toner of different charging characteristic is replenished from a cartridge later, it is apt to vary the image density or flies about itself.
Furthermore, assume a system of the type detecting a toner end condition with an optical sensor when the amount of toner deposition on a photoconductive element decreases. Then, the system is likely to detect a toner end condition despite that toner is present in a cartridge, if adequate aging is not executed.